Below is a complete section of my query. I am trying to order by t.age_group but the values don't lend themselves to being ordered the way I want it to be ordered.

The values can begin with O, R or U and I need to order them like this:

R, O, U,

Should I make a new table column for an ordering value, which can be assigned when the record is created or, can this query be amended to do what I need, with the existing data?

Code MySQL:
  JOIN ( SELECT live_product_id 
              , GROUP_CONCAT(
                           , t.age_group
                           , t.tariff
                           , t.tariff_terms_abbr
                           , t.currency
                           , tt.tariff_terms
                             ) ORDER
                                  BY t.age_group
                  SEPARATOR ';'
                               ) AS tariffs
           FROM tariffs as t
           inner join tariff_terms as tt
           on t.tariff_terms_abbr = tt.tariff_terms_abbr
            BY live_product_id
                                    ) AS tb